With the general acceptance of MPEG2 as a standard for the digital compression of video signals, many groups world-wide have developed or are developing coders or decoders; chip-sets are now commercially available and others have been announced. It is generally found, however, that existing circuit designs are inflexible and are directed only towards the requirements for standard definition television, typically main profile at main level.
It is an object of the present invention, to provide circuits--suitable for integration--which are flexible and which offer compatibility with higher profiles and levels of MPEG.
It is an object of certain aspects of the present invention to provide circuits--suitable for integration--which offer compact implementation of functions that cannot be implemented with existing coding and decoding chips or chip--sets.
It is still a further object of aspects of the present invention to provide circuit designs--suitable for integration--which can be used to implement in a cascadable form, functions including not only coding and decoding but also bitstream switching and editing.
It is explained in WO-A-9535628 that an information signal can with great advantage be provided from (for example) a decoder to a re-coder or other processing element downstream in the signal chain. The information bus may contain motion vectors and MPEG coding decisions which can be employed in re-encoding or later processing. The same disclosure introduces the concept of a coefficient domain which is the result of partial decoding of a compressed signal. It is found that certain functions, which would otherwise require decoding, processing and re-encoding, can be conducted more efficiently and with less errors in this coefficient domain.
It is a further object of the present invention to provide circuit designs suitable for integration--which take advantage of various features disclosed in WO-A-9535628.